Objective:

The changing climate is expected to impact particulate matter air pollution over the coming decades. The ability to predict and anticipate that change is of key importance for environmental management in the United States. In particular, changes in temperature, precipitation, biogenic emissions, or wildfires are expected to strongly modify the formation and lifetime of secondary organic aerosols (SOA). Modeling of these compounds in current chemistry climate models is very crude, and doesn’t provide the predictive capabilities needed to accurately quantify SOA sensitivity to climate perturbations. We propose to build a new SOA formation mechanism constrained from explicit chemistry and field measurements, and to apply the new mechanism to evaluate changes in SOA concentrations and spatial distribution resulting from changes in climate itself and climate-sensitive precursor emissions.

Approach:

We will perform explicit chemistry simulations using the state-of-the-science GECKO-A model to study gas-phase oxidation of organics emitted by major biogenic and anthropogenic sources. We will verify the results against chemically-speciated ambient oxidation flow reactor measurements in urban, forested, and biomass burning environments, including the amount of SOA formed, the destruction of SOA at long photochemical ages, and the evolution of the degree of oxidation with age. We will fit a reduced mechanism to GECKO-A results, and implement the new mechanism into the WRF-Chem regional and CESM global models to simulate the present day distribution of SOA, and evaluate both models against regional organic aerosol data over the U.S. Our new scheme will produce less volatile aerosols, and therefore is expected to provide a more realistic quantification of the contribution of long-range transport to SOA concentrations measured on the US West Coast. Finally we will perform global model simulations to quantify how SOA surface concentrations, spatial distribution and lifetime will change over the U.S. in response to changes in temperature, precipitation, biogenic and anthropogenic emissions. The impacts of future SOA on radiative forcing, public health, and visibility will be evaluated.

Expected Results:

We will provide, in the form of publications and code, a method to calculate the formation and properties of SOA in regional and global models, which is computationally efficient and constrained by fundamental chemistry and field measurements. Comparisons with the benchmark GECKO-A model will allow us to evaluate uncertainties and limits of applicability. The results will provide fundamentally new insights into the sensitivity of organic particles and vapors to changes in temperature (through better description of their volatility), precipitation (solubility), land use (dry deposition), emissions (yields constrained from chemistry and field measurements), and long-range transport (better represented ageing of organic vapors). This work directly addresses several goals of the solicitation seeking more accurate modeling tools that have the predictive capability needed for policy makers.

Supplemental Keywords:

Progress and Final Reports:

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.